Current asphalt blowing systems require a lot of space, are difficult to maintain, need a large volume of gases to operate, emit undesirable fumes, and require a scrubber to filter out such fumes.
Asphalt flux is the asphaltic material that is derived from crude oil. In addition to the hydrocarbons, asphalt flux sometimes contains additives such as waxes or inorganic salts like ferric chloride. Asphalt flux is usually delivered by large, heated pipeline, tankers, or railcars to the processing facility, where temperatures may range from 90° C. to 204° C. At the processing facility, the asphalt flux is typically pumped or piped into large heated storage tanks, usually kept at 51+ C. to 79° C. although some facilities store at temperatures as high as 230° C. Oil-fired, steam, or gas pre-heaters typically are used to maintain temperatures.
Asphalt air blowing is necessary for the production of converted asphalt flux into either of two roofing grades of asphalt, known as saturant grade and coating grade. These grades require the blowing process to achieve the desired softening points and to make them ready for coating or saturating the substrate roofing materials or shingles. The softening point of saturant asphalts is 0.40° C. to 74° C., while the softening point of coating asphalts is about 110° C. But the blowing of asphalt has been noted to be a primary source of organic emissions, including pivaloyloxymethyl (POM) emissions, in conventional asphalt blowing systems.
The configuration of a conventional blowing plant is shown in FIG. 1. Such a system typically includes an asphalt bulk supply tank 902, an asphalt blowing tank 904, an air or oxygen supply 906 to the asphalt blowing tank 904, a knock-out pot 908, and a finished-product bulk-storage 910. Materials exiting the knock-out pot 908 travel to a thermal oxidizer 912 or a knock-out oil storage tank 914. Such systems also generally include three asphalt process pumps 916 and two heat exchangers 918.
Existing designs typically have a vertical tank or horizontal asphalt blowing tank 904 and a sparger 920 that is either rotating or fixed. The sparger 920 has small holes in it, through which gases are passed to blow the asphalt. The conventional vertical tank configuration generally requires less gas than a conventional horizontal tank configuration due to the greater head height of the vertical tank.
Dire to the large size of existing tanks, they require a greater amount of heat and energy to maintain blowing temperatures required during the blowing cycle than would a smaller tank. The existing systems also require the spraying of steam or water onto the asphalt flux surface to help control the exothermic nature of the process and maintain the desired temperature of around 260° C. Overheating is also a problem in stirred tank designs, where it is critical to keep the asphalt flux at least 28° C. below its flash point as the asphalt is being blown (as specified by the U.S. Environmental Protection Agency in 1980). Due to the large volume inside the stirred tanks, it is also difficult to make sure all of the asphalt flux reaches the san temperature and has uniform gas distribution to induce the exothermic reaction.
Accordingly, there is a need for an asphalt blowing system that is safer, less volatile, more consistent, and more continuous than the conventional apparatus and systems. There is also a need for a system that takes up less space and is easier to operate and maintain.